[lycier]

Now I would challenge a robot.

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Result: 4♠S=

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Result: 3♠S-2
There are not differences between playing ♦10 and ♦9 {or ♦8} for human player when holds ♦AQT982, but there are some differences for Gibs.

[steve2005]

Gib and lycier never saw the danger.
On 3♦ somebody will have a singleton.
Must draw trump not finesse

[steve2005]

So why did West not find the entry to east's hand to get ruff in 1st example?
I mean besides the obvious answer that GIB can't signal.

[johnu]

 steve2005, on 2018-October-29, 09:17, said:

So why did West not find the entry to east's hand to get ruff in 1st example?
I mean besides the obvious answer that GIB can't signal.

The question you should ask is why did West find the entry in the 2nd example? Because declarer already played ♥A and presumably has ♦K and ♠A as well, so East having ♣K is highly likely.

In the 1st example, declarer has rebid 2♣, so not only has (likely) length in clubs (and short hearts), but more likely to have ♣K (and East is more likely to have ♥A because of longer hearts). Of course, that is bridge logic, not GIB logic, so nobody knows the real reason.